December 1, 2021

I, Science

The science magazine of Imperial College

Extremophiles thrive in the most uncomfortable places on Earth and beyond ...


From well below freezing to boiling water, from the crushing pressure in deep ocean trenches to the thin air above Mount Everest, many different types of life have adapted to live in extreme conditions – these, are the extremophiles. The benefits are great for those that can survive; there aren’t many competitors or predators where nothing else lives.

The solutions that different organisms have developed over millions of years are fascinating. Insects pump their bodies full of antifreeze to survive down to -150°C, witness the red flat bark beetle (Cucujusclavipes) that lives in northern Alaska. Sahara Desert ants (Cataglyphisbicolor) can survive a mid-day heat that reaches 60°C, albeit for only three to five minutes per day; they have silver bodies to reflect the heat, long thin legs and an accurate navigation system to get home quickly.

Deep in the ocean, Pompeii worms survive both high pressure and high temperature, living alongside volcanic vents at around 80°C. The worms have a symbiotic relationship with thermophilic bacteria, which might be how they survive.

However, the tardigrade, or water bear, wins the competition for a multicellular organism that can survive almost anything. It is a polyextremophile so can survive a variety of extreme environments, from very close to absolute zero (less than -270°C) up to 150°C. They have been known to survive in a dehydrated, hibernation-like state for over a hundred years without food or water. Neither high nor low pressures are a problem for these creatures, which have survived in space, and at pressures six times higher than the bottom of the ocean, even surviving radiation blasts.

Why they have evolved to be this resistant is still a mystery. Their normal habitat is moss and lichen – not the most challenging of environments. Although why is not the interesting question here; scientists are currently looking at how they survive these conditions and what we could learn from their physiology.

Bacteria and microorganisms are another area for research, psychophilic (cold-loving) and thermophilic (heat-loving) microorganisms are being studied to find new enzymes and reactions that are optimised for different temperatures and that could be used in industrial reactions. For example, PCR (polymerase chain reaction) for DNA amplification is not possible without the thermostable enzymes that survive cycles at 90°C, originally found in the bacterium Thermusaquaticus.

If life can survive more extreme conditions, there are more places to look, including in our solar system. Endoliths are organisms (including bacteria, lichen, algae and amoeba) that live in rock or minerals but one species has been found that lives for millions of years by slowing its reproduction cycle – each generation has a reproduction cycle every 10,000 years. Astrobiologists hope that these organisms could potentially live on other planets, for example, endolithic conditions have been found on Mars, and so studying them is important in the search for extra-terrestrial life. Extremophiles have implications for panspermia, the theory that life does exist throughout the universe and is distributed by comets, meteoroids and planetoids. For this to occur, life would have to survive conditions in space, as well as ejection from one planet and entry to another – extremophiles are the prime candidates for this.

From the deepest oceans to deeper space, extremophiles are telling us ever more about the world we live in and, potentially, those of other life-forms.


IMAGE: OnceAndFutureLaura